Paraneoplastic disorders ace uncommon but clinically important complications of a large number of neoplasms. Most paraneoplastic syndromes are thought to have an autoimmune etiology, although the weight of evidence supporting autoimmunity vanes among syndromes. Prompt diagnosis of a paraneoplastic disorder can increase the likelihood of a favorable neurologic and oncologic outcome. This article reviews the; clinical features, autoimmune aspects, diagnostic approach, and treatment options for patients with paraneoplastic disorders affecting the spinal cord, motor neurons, neuromuscular junction, and muscle. Part 2 of this review, to be published in the next issue, will discuss the paraneoplastic neuropathies.